5G Isn't Going Indoors Anytime Soon

Most of today's 5G networks in the US, particularly those running in high-band spectrum, are specifically intended for customers who are walking around outside. When 5G subscribers go inside, they definitely won't get 5G. In fact, they might not even get 4G.

And, according to a wide range of executives in the wireless industry, that situation is not going to change anytime soon.

"It's super early" to talk about 5G indoors, said Slavko Djukic, CTO of Zinwave, a company that works with wireless network operators and building owners to install cellular networks inside buildings.

"A way to distribute the 5G signal inside of a building simply doesn't exist yet," added Jeremy Edalgo, director of wireless sales and engineering at McKinstry, which is a nationwide construction and engineering company that handles everything from mechanical to electrical to plumbing work. The company has worked on 10,000 buildings around the country.

"We think it's very feasible" to take 5G indoors, said Tom Anderson of ATIS, an association that develops communications standards for telecom providers in North America. However, "it's not quite there yet."

This is important because, according to a widelycitedstatistic, around 80% of all mobile data traffic is consumed indoors.

A new type of network
To put the indoor 5G problem into perspective, you have to go back more than a decade to the beginnings of 4G. That's when wireless services became important enough for a majority of building owners to begin thinking about how to make sure cell phones reliably work inside.

"In the beginning [of 4G], letting 700MHz [outdoor transmissions] crank through the building was good enough because people didn't even know how dependent they would be on these devices," said Verizon's Adam Koeppe at a recent investor event. "And then what happened over time? The network design actually shifted from 'outside-to-in' for in-building coverage to 'inside-stays-inside' and 'outside-stays-outside.'"

Meaning, the wireless industry has slowly been bifurcating between two types of wireless networks: Those designed for outdoor usage (where signals also penetrate most small buildings) and those designed specifically for indoor usage.

Indoor cellular networks -- often using Distributed Antenna Systems (DAS) -- were first championed by giant venues like airports and stadiums where lots of people used their phones. Outdoor signals often can't reach inside those kinds of massive facilities. In those cases, wireless network operators often footed a large chunk of the DAS installation bill because they wanted to make sure their services would work in those high-profile locations.

And, according to Verizon's Koeppe, it's those locations that will likely get 5G first. "Stadiums are ripe for that kind of thing," he said, adding that he expects 5G equipment for in-building coverage to become available "towards the end of this year."

Already AT&T has announced that its AT&T Stadium in Arlington, Texas, will be among the first such venues to sport an indoor 5G network.

As 3G transitioned to 4G and smartphones became indispensable, indoor cellular coverage quickly moved from a nice-to-have to a must-have for an increasing number of building and real estate managers. Indeed, a 2015 survey by network equipment company CommScope found that nearly half of all architects globally have begun to design buildings with in-building cellular networks in mind.

Re: Data on 5G IndoorIt appears that indoor 5G will follow the way Wi-Fi had to walk: shifting from 2.4 GHz to 5 GHz brought more frustration than benefits. Simple physics tells that propagation decreases roughly with the square root of frequency (more or less, add or take a water peak or two), and operation at millimeter waves decreases the reach/coverage even further.

I assume that in a few years, we'll start hearing about "mesh 5G" -- analogous to mesh Wi-Fi -- as the only way to guarantee proper indoor coverage and performance. (Just remember I used this term first. :)

I am also pretty sure that the debate about health implications will heat up (finally). One does not have to have a PhD in physics to understand that signal attenuation translates to absorption -- in walls, water tanks, our pets and our bodies.

Re: Data on 5G IndoorFormally correct, I should have stated that the attenuation coefficient is roughly proportional to the square root of frequency (no, not the square of frequency). BTW, the Friis formula was shown to be an antenna effect and not a wave-propagation effect (for example, see https://www.dsprelated.com/showarticle/62.php).

The dependence on square root of frequency is valid for any propagation medium with non-zero conductivity, i.e. for everything but vacuum. If you are tempted to argue that (dry) air is close to that, I will come back with adding a few obstacles (such as wood, concrete, anything with metal or presence of water) into the model, and point you to the calculation of strength of non-absorbed (propagated through obstacles) signal -- which will be eventually closely dependent on "remainders" after skin effect-related losses.

In indoor environments with obstacles that do not completely block the transmition (these would be concrete, chicken-wire, metals, water, etc), the remaining transmitted signal depends on electrical conductivity of obstacles, and is mostly affected by losses described best by skin-effect formulas -- which are given/approximated by the square root of the frequency.

Interestingly enough, it turns out that specific "lower"-frequency ranges can as well be approximated by the square root, even in obstacle-free spaces, and the approximation aligns well with empirical measurements (in indoor environments).